Model Tests on Improvement of Holding Power and Dragging Stability of Anchor

Abstract

Main object of this investigation is to find a prototype of ship's anchor which has larger holding power and dragging stability by systematic model tests. For the comparision of holding power characteristics, coefficients λ, α, μ, and etc. were used, where the coefficient of holding power λ is a ratio of maximum dragging pull at zero speed in pull-speed curve to weight of anchor, the coefficient of dragging stability α is a ratio of the area enclosed with the measured curve of holding power vs. dragging distance to the area multiplied the maximum dragging pull by dragging distance and the coefficient of holding characteristics is μ is λα. From the results of experiments in sand bottoms, the authors obtained a new prototype of ship's anchor, KS-7 type, having superior holding characteristics. Futhermore, the effect of shape factors of anchor on the holding characteristics are investigated, and the results are as follows : 1) The holding power is more affected by the vertical projected area of fluke (A_<fy>) than the vertical projected area of anchor-head (A_y). 2) As to the effect of shape factors on the dragging stability, the most important factor is b/h, the next is e/b, and e/h has almost no effect, where b is the width of crown-bed, h is the length of fluke, and e is the gap between the tip of both flukes. 3) It seems that the anchor having large holding power is not good in the dragging stability, and that the relation between μ and A_y/A_<fy> is also similar.